This project will involve a prospective analysis of the cognitive/neuropsychological changes accompanying the administration of prophylactic cranial irradiation in patients with small cell lung cancer receiving combinations of chemotherapy, surgery, and chest irradiation compared to a group of patients who receive chemotherapy alone and a group of non-medical control subjects. This study is important since prophylactic cranial irradiation has been shown to prevent relapses. Patients with small cell lung cancer who demonstrate a complete response will be administered prophylactic cranial irradiation as part of their standard clinical care. Cognitive/neuropsychological functioning will be evaluated using a battery of neuropsychological instruments selected on a priori theoretical considerations for their sensitivity to subtle CNS dysfunction and their ability to provide data on how the patients' activities of daily living might also be affected by the sequelae of prophylactic cranial irradiation. The prophylactic cranial irradiation patients will receive a Practice Effects Neuropsychological Assessment and a Baseline Neuropsychological Assessment prior to the initiation of prophylactic cranial irradiation therapy. Patients will then be assessed at two follow-up evaluations: three months and six months post-prophylactic cranial irradiation. The subjects in the two control groups will be matched to the prophylactic cranial irradiation patients on age and sex. In addition to evaluating each subject's quantitative neuropsychological performance using the assessment battery, each subject will complete a qualitative neuropsychological performance questionnaire after each of the four neuropsychological assessments. This procedure will determine whether or not prophylactic cranial irradiation patients are "aware" of the degree of any cognitive changes. The immediate objectives of this project are: (1) to determine the presence and severity of neuropsychological changes secondary to prophylactic cranial irradiation; and (2) to ascertain whether patients are "aware" of these changes by comparing their quantitative and qualitative neuropsychological performances. A long-term goal is to determine the schedule of prophylactic cranial irradiation treatment so as to minimize the negative neuropsychological sequelae while preventing relapses.